Engines have been described utilizing multiple injector locations with different fuel types. One example is described in the papers titled “Calculations of Knock Suppression in Highly Turbocharged Gasoline/Ethanol Engines Using Direct Ethanol Injection” and “Direct Injection Ethanol Boosted Gasoline Engine: Biofuel Leveraging for Cost Effective Reduction of Oil Dependence and CO2 Emissions” by Heywood et al. Specifically, the Heywood et al. papers describe directly injecting ethanol to improve charge cooling effects, while relying on port injected gasoline for providing the majority of combusted fuel over a drive cycle. Thus, it has been demonstrated that the selective use of a knock suppressing substance such as ethanol with gasoline fueled engines can reduce knock during boosted operation, particularly where the engine may otherwise be knock limited.
The inventor of the present application has recognized various issues with the above approach. As one example, the engine output may be significantly reduced where the availability of the knock suppressing substance on-board the vehicle is low. For example, even when the engine has sufficient fuel reserves remaining on-board the vehicle, the depletion of the knock suppressing substance may once again cause the engine to be knock limited, thereby reducing the level of boost that may be provided to the engine. This reduction in engine output, under some conditions, may surprise the vehicle operator or may cause dissatisfaction with the performance of the vehicle.
As another example, where the knock suppressing substance is separated on-board the vehicle from a fuel mixture, the consumption of the knock suppressing substance at a rate that is greater than the separation rate may likewise cause the knock suppressing substance to eventually become exhausted. Thus, the vehicle operator may attempt or may be unable to initiate a vehicle control operation that is no longer practicable due to the reduced availability the knock suppressing substance. Alternatively, with each of the above examples, if the engine is instead permitted to be operated in a state where knock occurs without the use of the knock suppressing substance, engine damage may occur, or noise and vibration harshness (NVH) as a result of the engine knock may again cause dissatisfaction with the vehicle operator.
In response to at least the above issues, the inventor has provided as one example, a hybrid propulsion system for a vehicle including at least one drive wheel. The system comprises an engine including at least one combustion chamber; a motor configured to selectively propel the vehicle via the drive wheel; a fuel system configured to deliver a first substance and a second substance to the combustion chamber in varying relative amounts, wherein the first substance includes a fuel and the second substance includes a greater concentration of a knock suppressing substance than the first substance; and a control system configured to operate the fuel system to vary the relative amounts of the first substance and the second substance delivered to the combustion chamber in response to an operating condition while operating the motor to propel the vehicle.
Additionally, the inventor has provided, as another example, a method of operating a hybrid vehicle propulsion system including an engine and a motor coupled to at least a drive wheel of the vehicle. The method comprises delivering gasoline and alcohol to the engine in varying relative amounts responsive to an operating condition; varying an amount of energy stored in an energy storage device operatively coupled to the motor responsive to a condition of the fuel system.
In this way, the utilization of a knock suppressing substance such as an alcohol can be coordinated with other sources of vehicle propulsion, including an electric motor or other suitable drive motor, enabling a more consistent drive feel for the vehicle operator for a variety of operating conditions, such as where the availability of the knock suppressing substance or the amount of energy stored by the motor's energy storage device are reduced.